The present invention relates to a method for the automatic measurement of fluid flow with the aid of an electronic controller. The invention particularly relates to the accurate measurement of fluid flow rates over a very wide range.
The prior art is replete with meters and measuring devices for measuring variable fluid flow rates within a piping system. Many of these devices have been incapable of accurately measuring the flow rate of the fluid when the flow rate varies over a wide range. U.S. Pat. Nos. 2,425,720, 2,607,640, 2,764,022, 4,100,799, and 4,100,800 all disclose devices which can measure fluid flow rates over a wide range by utilizing two mechanical flow rate measuring devices, one for low flow rates and the other for high flow rates.
Small thermally sensitive resistor elements of the semiconductor type have been employed in flow indicators. These thermistors, temperature-dependent resistor fluid sensors, operate by correlating the temperature of the resistor with the fluid flow rate. An electrical current may be passed through such an element at a constant voltage, thus heating the element to a temperature higher than ambient temperature. The rate of heat dissipation from the element and, accordingly, its ultimate temperature, is proportional to the velocity of fluid flow past the element. The change in current flowing in the circuit as the resistance of a thermally sensitive element changes with temperature may be used as a measure of flow velocity. U.S. Pat. No. 4,043,196 discloses a method for fluid flow measurement which utilizes a temperature sensitive resistive element disposed within the fluid flow path. The patent suggests that the information from the thermistor may be used in a digital or analog read-out, a storage means, or such other apparatus or combination thereof which may appropriately utilize the mass
It is an object of the present invention to provide a device which is capable of accurately measuring fluid flow rates over a wide range with the aid of an electronic controller. Another object of the invention is to provide a method for measuring fluid flow employing a thermally sensitive electrical resistance element such as a thermistor, diode, transister, etc. in combination with other elements whereby the method is adapted to accurately measure high as well as low rates of fluid flow.